Evaluation of passive integrated transponder tags for marking the bullhead (Cottus gobio), a small benthic freshwater fish: effects on survival, growth and swimming capacity

This study examined potential adverse effects of surgically implanted passive integrated transponder (PIT) tags (12 × 2.1 mm) on bullhead (Cottus gobio L.) of three different length‐classes (I: 50–64 mm, II: 65–79 mm, III: 80–94 mm). During a 7‐week laboratory experiment, the rate of PIT tag loss, incision closure time, survival, growth and swimming capacity were tested. The PIT tag weight to fish body weight ratio varied between 1.04% and 4.85%. The mean incision closure time differed significantly among length‐classes and varied between 2.8 (I) and 4.3 (III) weeks. Nevertheless, PIT tag retention did not differ among length‐classes and was ≥90%. The survival of untagged, sham‐tagged and PIT‐tagged bullheads was ≥90% and did not differ within or among length‐classes. Finally, within each length‐class, there was no difference in growth and swimming capacity among treatments. Hence, these results suggest the applicability of PIT tags for individually tagging bullheads ≥50 mm.